The Lewis and Clark Expedition lasted 862 days from its departure in 1804 to its return in 1806.
Also called the Corps of Discovery Expedition, it was commissioned by President Thomas Jefferson after the Louisiana Purchase. Meriwether Lewis and William Clark led the group westward from the Missouri River to the Pacific coast and back.
The expedition departed from Camp Dubois near present-day Hartford, Illinois, on May 14, 1804. It reached the Pacific Ocean in 1805 and began the return journey from Fort Clatsop on March 23, 1806. The members returned to St. Louis on September 23, 1806.
The journey combined exploration with scientific observation, mapping, diplomacy, and information gathering. Sacagawea traveled with the party and assisted as an interpreter and guide. The expedition did not “discover” an empty wilderness: Native nations already lived throughout the region and shaped the travelers’ progress.